[FFmpeg-devel] [PATCH] avcodec/avpacket: ensure the packet is writable in av_shrink_packet()

[James Almer]

On 3/24/2018 6:46 PM, wm4 wrote:
> On Sat, 24 Mar 2018 18:11:53 -0300
> James Almer <jamrial at gmail.com> wrote:
> 
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>> This is a good time to deprecate this function and introduce a
>> replacement using the correct av_packet namespace and this time
>> returning an int.
>> What would be better
>>
>> int av_packet_shrink(AVPacket *pkt, int size);
>>
>> Or
>>
> 
>> int av_packet_resize(AVPacket *pkt, int size);
> 
> Seems better.
> 
>>
>> The latter would be a combination of both the current shrink and grow
>> functions.
>>
>>  libavcodec/avpacket.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
>> index 0693ca6f62..7faa082395 100644
>> --- a/libavcodec/avpacket.c
>> +++ b/libavcodec/avpacket.c
>> @@ -100,9 +100,12 @@ int av_new_packet(AVPacket *pkt, int size)
>>  
>>  void av_shrink_packet(AVPacket *pkt, int size)
>>  {
>> +    int packet_is_writable;
>>      if (pkt->size <= size)
>>          return;
>>      pkt->size = size;
>> +    packet_is_writable = !av_packet_make_writable(pkt);
>> +    av_assert0(packet_is_writable);
>>      memset(pkt->data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
>>  }
>>  
> 
> LGTM

Ok, but i just realized that i can't apply this without first writing an
internal variant specifically for the encoders that makes sure pkt->data
!= avctx->internal->byte_buffer before trying to do anything, otherwise
the supposed benefits of that weird internal buffer code in
ff_alloc_packet2() would be lost.

Will look at that later.